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Journal of the Geological Society; 2009; v. 166; issue.4; p. 811-823;
DOI: 10.1144/0016-76492008-042
© 2009 Geological Society of London

Thematic set: Eclogite-facies rocks: a window into geodynamics and lithospheric evolution

On the occurrence and boron isotopic composition of tourmaline in (ultra)high-pressure metamorphic rocks

Horst R. Marschall1, Andrey V. Korsakov2, George L. Luvizotto3, Lutz Nasdala4 & Thomas Ludwig3

1 Department of Earth Sciences, Wills Memorial Building, Queen's Road, University of Bristol, Bristol BS8 1RJ, UK
2 Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Science, Koptyug Pr. 3, Novosibirsk 630090, Russia
3 Mineralogisches Institut, Universität Heidelberg, Im Neuenheimer Feld 236, D-69120 Heidelberg, Germany
4 Institut für Mineralogie und Kristallographie, Universität Wien, Althanstr. 14, A-1090 Wien, Austria

*Corresponding author (e-mail: Horst.Marschall{at}bristol.ac.uk)

The extensive P–T stability and the high chemical variability of tourmaline (Tur) together with its common occurrence in metasediments proves its high potential for petrological and (isotope) geochemical studies on fluid–rock interaction in subduction- and collision-related rocks. This paper reviews the occurrence, major element chemistry and boron isotopic composition of Tur in high- and ultrahigh-pressure metamorphic (UHPM) rocks. In addition, it presents a new discovery of coesite-bearing Tur (schorl) from the Erzgebirge (Germany), as well as Tur (dravite) related to the retrograde history of coesite- and diamond-bearing rocks from the Erzgebirge and the Kokchetav Massif (Kazakhstan). The scarce data on worldwide occurrences of (U)HPM Tur reveal a high occupation of the crystallographic X-site (dominated by Na) and the possible presence of excess B, with little further distinctiveness in its major element composition when compared with Tur from medium-grade rocks. High K2O contents in Tur are probably not related to UHP growth or equilibration. The B isotopic composition of (U)HPM Tur ranges in {delta}11B from –16 to +1{per thousand}, with many samples in or below the range of continental crust. In contrast, Tur formed during retrograde fluid influx typically shows high {delta}11B values (up to +28{per thousand}), suggesting heavy-B fluids infiltrating the exhuming (U)HPM units. Coesite inclusions in Tur, characterized by Raman spectroscopy, are regarded as the best indicator for its UHP stability.

Supplementary material: Analytical methods, tourmaline compositions and boron isotope values are available at http://www.geolsoc.org.uk/SUP18354.





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A. Ertl, H. R. Marschall, G. Giester, D. J. Henry, H.-P. Schertl, T. Ntaflos, G. L. Luvizotto, L. Nasdala, and E. Tillmanns
Metamorphic ultrahigh-pressure tourmaline: Structure, chemistry, and correlations to P-T conditions
American Mineralogist, 2010; 95: 1 - 10.
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